"Crazy by Gnarls Barkley has made pop history as the UK's first number one song based on download sales alone. Until this month, download sales could only count towards a chart position if the song could also be bought in shops.

But under new rules, downloads can be counted as long as physical copies go on sale the following week.

The song, used in ads for Zane Lowe's Radio 1 show, has been downloaded more than 31,000 times on all internet sites, a spokesman for HMV said."

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